In 1994 he joined the Ministry of Defence as Colonel Army Plans.[9] In December 1995, after completing the Higher Command and Staff course, he was promoted brigadier[10] and then became Commander of the 4th Armoured Brigade in Germany.[2] He became Chief of Joint Force Operations at the Permanent Joint Headquarters in 1998. In this role, as the default commander for short notice expeditionary operations, he commanded the UK Contingent in East Timor as part of INTERFET in 1999 and twice commanded a UK Joint Task Force in Sierra Leone in 2000.[4]

Allegations surfaced in September 2009 of a Labour Party plot to smear the general because his daughter worked for the Conservative Party. The threat to target Richards, who had taken up his new job just nine days before most of the reports appeared, was widely reported to have been one of the real reasons that Labour MP Eric Joyce resigned as an aide to Defence Secretary Bob Ainsworth.[22]

In February 2010, Richards said that a "turning point" had been reached in the battle against the Taliban. He suggested troop numbers could begin to decline as early as 2011 while the majority would be withdrawn by 2015. Richards said "we are now seeing some very optimistic signs" in the latest military offensive, Operation Moshtarak (togetherness), in Helmand. The Taliban had been forced to give "serious consideration" about continuing the fight. Richards said that: "We expect the military conflict to trail off in 2011," who was visiting British front-line forces for the first time since taking command of the Army last year. "The combat role will start to decline in 2011, but we will remain militarily engaged in training and support roles for another five years, and we will remain in a support role for many years to come."[23]

Richards said that "The Taliban is now beginning to realise that they can lose this war, which was not the view they had a year ago. We have to reinforce the view that they can, and will, be beaten."[23] In 2010, however, he also stated in a radio interview that "I think there's no reason why we shouldn't be looking at [talking to the Taliban] pretty soon".[24][25]

On 14 July 2010, the Ministry of Defence announced that in October 2010 Richards would become the next Chief of the Defence Staff in succession to Air Chief Marshal Sir Jock Stirrup.[26] Downing Street, in a press statement to announce the intended ennoblement of Sir Jock, also announced in the same release that Sir David would take up his new post as Chief of the Defence Staff on Friday 29 October 2010, immediately after the retirement of Sir Jock.[27]

In November 2010, General Richards said there was no desire to "open up another front" in the Middle East but suggested that in future it "might be" necessary. David Cameron told Parliament that Britain would "take every step to cut out the terrorist cancer that lurks in the Arabian Peninsula", but Gen Richards said an intelligence-led approach was the current strategy. Richards added: "Clearly, the primary agencies dealing with this are our intelligence and security agencies. But the military are already helping with their [the Yemenis'] training. I don't think we want to open up another front there and nor do the Yemenis want us to do that. So we have to find other ways of doing these things and in the meantime making sure Afghanistan doesn't revert to becoming, if you like, a 'second Yemen' – that is the Army's primary duty at the moment. Our role is to remain very close to them, to help them where they most need it and in the meanwhile focus our efforts on Afghanistan and assisting Pakistan to ensure they don't become the threat Yemen is beginning to be.[28]

In May 2011, General Richards and other senior NATO officers expressed a wish for backing from member states to intensify the war effort in Libya by directly targeting Col Gaddafi's regime, rather than simply protecting Libyan civilians. "The military campaign to date has been a significant success for NATO and our Arab allies, but we need to do more. If we do not up the ante now there is a risk that the conflict could result in Gaddafi clinging to power," said Gen Richards. He added that, while NATO forces were not targeting Col Gaddafi directly, he could nevertheless become a legitimate target if he was caught directly attacks against Libyan civilians. "The United Nations resolution allows Nato to use 'all necessary means' in Libya," he said. "We are not targeting Gaddafi directly, but if it happened that he was in a command and control centre that was hit by Nato and he was killed, then that is within the rules."[29]

During the Syrian Civil War Richards drew up plans to train and equip a Syrian rebel army of 100,000 to overthrow President Bashar al-Assad, as an alternative option to the government’s plan for limited direct military involvement. The plans were rejected by the National Security Council as too ambitious.[30] Ultimately on 29 August 2013, parliament refused to support the government's plan to participate in military strikes against the Syrian government.[31]

On 26 June 2014, Richards said that Britain's Armed Forces will be like a banana republic's if the Ministry of Defence kept cutting costs, and criticised the “bean counters” who cut perks for his successors. Defence Secretary Philip Hammond 'would never be a good soldier'. Richards was concerned about a controversial plan to replace regular troops with reservists. On pay to soldiers, he said[36]

“

“But because we look after them and because it’s socially at every level acceptable to be in the Army, whether you a private in the greenhouse from Yorkshire or the heir to the throne and you are a captain in some smart organisation, the fact is there is a consensus that it’s a good to be in the armed forces. If you lose that, because you don’t look after your people well, you will have an army, a navy and an air force, but it will be the sort of army, navy and air force with which we don’t associate with the British, that you associate with banana republics ultimately. We have outstanding people and we need to look after them.

”

On 7 October 2014, Richards criticised the contemporary Western strategy employed to defeat ISIS. He said that air strikes are[37]

“

never going to be sufficient. The trouble is that once they get into built-up areas it's very difficult for air power alone to dislodge them and obviously all our air forces take a lot of trouble about not causing civilian casualties.